Annual production of cheese whey in the United States was approximately 80 billion pounds in 2006 (U.S. Department of Agriculture, National Agricultural Statistics Service, Washington, D.C.). This by-product of the cheese industry was once regarded as a waste effluent and was used as cattle feed and spread on land. Whey, however, has enormous potential not only as a source of nutritionally exceptional food proteins, but as a rich source of pharmacological, immunological, antibacterial, and bioactive agents. Shown in FIG. 1 is the list of various high value functional proteins and bioactive components that can be isolated in large quantities from cheese whey.
With the advent of ultrafiltration in the late 1970's, a significant portion of whey is now converted into whey protein concentrates. Whey protein concentrate 80 (WPC80, 80% protein on a dry basis) is manufactured by extensive ultrafiltration and diafiltration of crude whey to reduce the non-protein components, especially the lactose content. WPC80 is a homogeneous, free-flowing powder. WPC80 has become a popular protein ingredient because is contains highly nutritive proteins, it is soluble over a wide pH range, and has good gelling, and water-binding characteristics. It is used in dairy, bakery, meat, snacks, confectionary, infant formulae, and other food and nutritional products. It has the potential for use in sports nutrition, energy bars, low carbohydrate diet formulae, yogurt, ice cream, and dry mixes.
Commercial WPC80 typically contains 80 to 82% protein, 4 to 8% lactose, 4 to 8% fat, 3 to 4% ash, and 3.5 to 4.5% moisture. Commercial WPC80 exhibits a wide variation in functional properties even from the same processing plant (Holt et al., 1999). Although most WPC products are generally tasteless immediately after production, they develop a typically stale, oxidized off-flavor during storage. The off-flavor is due to a series of complex, inter-related chemical reactions that include lipid oxidation and Maillard browning (Morr & Ha, 1991). The development of the off-flavor during storage is one of the factors that limit more extensive use of WPC80 in various food products (Carunchia Whetstine et al., 2005).
Most of the quality defects, such as discoloration, off-flavor development, poor solubility, turbidity, poor foaming and emulsifying properties, etc., that arise during storage of WPC80 can be traced back to its high lipid content. The residual lipid fraction in WPC80 comes from fragments of milk fat globule membrane (MFGM) and very tiny intact fat globules (Vaghela and Kilara, 1996). These small, stable colloidal particles remain in the whey after clarification. The lipid content of isolated MFGM is about 72% and the phospholipid content is about 30% of the total lipids found in whey (Fong et al., 2007). The MFGM fragments are concentrated and retained with the protein during manufacture of WPC80 using ultrafiltration and diafiltration processes. During ultrafiltration, the MFGM fragments foul the ultrafiltration membrane elements. The fouling significantly decreases the permeate flux rate and increases the frequency of equipment cleaning cycles. This, in turn, increases in energy cost to produce WPC80. In the final product, the lipids and phospholipids impart turbidity when the WPC80 powder is reconstituted into solution. This is a highly undesirable quality in protein drink-type products. Lipids and phospholipids also impair the foaming and emulsifying properties of WPC80.
More importantly, oxidation of the MFGM lipids during storage of WPC80 results in the development of off-flavors. Some of these off-flavor compounds are aldehydes and ketones, which undergo carbonyl-amine reactions with amino groups of proteins. These chemical changes cause discoloration in the WPC80 powder and adversely affect the functional properties of whey proteins, e.g., foaming, emulsification, gelation, solubility, and turbidity (Vaghela and Kilara, 1996). All of these undesirable changes in WPC during storage limit its usefulness in a variety of food products.
Several methods have been reported in the past to remove lipids from cheese whey (Breslau et al., 1975; Grindstaff & Ahern, 1975; Maubois, et al., 1987; Lehmann & Wasen 1990; Rinn et al., 1990). The efficacy of these methods have been reviewed (Morr & Ha, 1991). However, most of these methods cause complete denaturation and insolubilization of whey proteins. Denaturation and insolubilization impair most of the functional properties of the proteins. See also U.S. Pat. No. 3,560,219, issued Feb. 2, 1971, to Attebery. In this approach, the whey is treated by adjusting its pH to a value of above 6 (preferably from 7.0 to 7.5) and adding a divalent metal ion to a concentration of at least 0.075 molal.
In an earlier attempt to address the longstanding issue of quality defects caused by MFGM lipids in WPC80, the present inventor had previously developed a simple process to flocculate MFGM using colloidal chemical principles. The colloidal stability of MFGM in cheddar cheese whey (and other types of cheese whey) is due primarily to their highly negatively charged surface. Neutralization of these negative charges under specific conditions using a poly-cationic polymer can induce flocculation of MFGM fragments. In previous work co-authored by the present inventor, it was shown that chitosan (a poly-glucosamine polymer) selectively binds to and causes flocculation of MFGM fragments. (See U.S. Pat. No. 5,436,014, issued Jul. 25, 1995, to Damodaran). According to this method, adding about 0.01% (w/v) chitosan using a stock solution containing 1% chitosan in 10% acetic acid to cheddar cheese whey at pH 4.5 resulted in the formation of a chitosan-MFGM complex. Upon incubation for 30 min at 25° C., the complex flocculated and precipitated. The precipitate could then be removed by centrifugation. The resulting clarified whey was crystal clear in appearance and contained almost all the whey proteins, including IgG. The clarified whey also had a fat content of less than 0.26 g/100 g protein. This chitosan process can be carried out with 5-fold concentrated whey.
The chitosan process completely removes lipids from cheese whey, allowing efficient processing of the crystal clear whey into fat-free WPC and WPI. The WPC80 obtained using the chitosan process is very stable against discoloration during storage compared to commercial WPC80, as shown in FIG. 2. This also categorically confirms that oxidation of MFGM lipids and a series of reaction of the resulting carbonyl compounds with amino groups of proteins through the Maillard reaction is the principal cause of discoloration and off-flavor development in WPC during storage.
Although the chitosan process is simple and produces highly functional WPC and WPI, whey processors are unable to use this technology in the United States because chitosan is not yet approved as a “GRAS” (generally regarded as safe) substance in the U.S. (although chitosan has GRAS status in Europe and Japan). Furthermore, recovery of MFGM from the chitosan-MFGM complex is not effective under mild conditions. Thus, there is still a long-felt and unmet need to develop a simple process to remove MFGM from cheese whey, thereby enabling cost-effective and energy-efficient production of high quality WPC80 and WPI. The unmet need is two-fold: (1) to reduce filter fouling by MFGM lipids, thereby decreasing the cost of whey protein production; and (2) to remove or to decrease significantly the concentration of MFGM lipids in the final whey protein concentrate product, thereby limiting off-flavor formation and discoloration of the whey protein concentrate.